A potentially cancer-causing substance formed during cooking at high temperatures has been found in a range of Hong Kong products.

But the food-safety watchdog says people's average daily intake is unlikely to cause problems.

High levels of 3-MCPD in fatty acid ester form have been found in food such as biscuits, snacks and Chinese pastry, the Centre for Food Safety said yesterday.

But it said an adult's average daily exposure to the substance was 0.20 to 0.53 micrograms per kilogram of body weight - well below the maximum tolerable intake of 2 micrograms per kilogram.

However, the centre urged consumers to ensure they eat a balanced diet with a wide variety of fruit and vegetables.

It said the International Agency for Research on Cancer had classified 3-MCPD - named for its chemical components - as "possibly carcinogenic to humans" because experiments had found it could cause cancer in animals.

"No data is currently available for carcinogenicity of 3-MCPD in humans. However, it would affect the kidney, the central nervous system and the male reproductive systems of rats," a spokesman for the centre said.

The ester is formed when foods containing fat and salt are processed at high temperatures in frying, deep frying, roasting and baking.

Thermally processed foods and refined fats and oils are the most significant sources of 3-MCPD fatty acid esters, the centre's report said.

In the tests, conducted last year and this year on 300 samples from the local market, higher levels of the substance were found in biscuits, fats and oils, snacks, and Chinese pastry. Breakfast cereal, nuts and seeds were found to contain relatively low levels.

Extra virgin olive oil was the only oil found to be free from the toxic substance, while refined oils contained higher levels than grapeseed oil and peanut oil.

Recent international reports also suggest 3-MCPD is found in a range of food products including French fries, toasted bread, salty crackers and roasted coffee.

It could be detected in items such as soy sauce, oyster sauce, fish sauce, instant noodles, garlic powder, spice mixtures and soup mixes, say other studies.

This article appeared in the South China Morning Post print edition as Cancer link to foods cooked using high heat